Method of making tennis balls



p 1953 J. ANDERSON ET AL METHOD OF MAKING TENNIS BALLS Filed Nov. 28, 1950 Patented Sept. 15, 1953 2,652,094 METHOD or MAKING TENNIS nAL s John Anderson, Sutton Coldfield, and Ronald Stansfield Goy, Castle Bromwich, Birmingham,

England, assignors to Dunlop Tire and Rubber N. Y., a corporation of Corporation, Bulfalo New York Application November 28, 1950, Serial No. 198,012 I In Great Britain Novemberi30, 1949 12 Claims. (01. 154 16) This invention relates to tennis and like inflated balls and to methods of making such balls.

A conventional tennis ball has heretofore comprised an inflated rubber core provided with an outer covering of Woven and felted fabric having usually one or more seams. The prefelted fabric portions are stuck to and molded on the core and quickly become shaken down in play with the result that the optimum playing characteristics of the ball are comparatively short lived, i. e., its dynamic properties alter quite rapidly in use, and after perhaps only a few games the ball is rendered unsuitable for use in high class tournament play.

tennis ball which does not suffer from the rapid change in playing characteristics exhibited by the conventional ball during shaking down of the cover and provides a method of making such balls which is convenient and more economical than methods of making conventional seamed tennis balls.

According to the invention a method of making a textile covered ball having an inflated core comprises covering an inflated core with a single thickness of composite yarn comprising a central thread wrapped with a helix of yarn or roving of felta ble material, effecting adhesion of the yarn to'the core and raising and felting the covering in position on the'core.

The invention is illustrated by way of example a in the accompanying drawings in which Fig. 1 illustrates a composite yarn 'used in the production of tennis balls by our invention Fig. 2 is a view of a tennis ball core partly wrapped with composite yarn;

Fig. 3 is a fragmentary section of a core after wrapping and Fig. 4 is a fragmentary section of a ball the composite yarn has been felted.

The composite yar'n' l shown in Fig. 1 comprises a central thread 2 of suitable materialsuch as cellulose acetate wrapped with a close helix of wool roving 3. The central thread 2 is of 1100 denier and the roving 3 consists of fifteen untwisted wool rovings of 5 West of Englah'ds count, twisted together with 1.5 2 T. P. 1. (turns per inch). The twisted rovings are wound onto the central thread 2 in a right circular helix of- 4.5 T. P. I.'to provide a substantially balanced composite yarn. To ensure that the composite yarn is in a substantially relaxed condition, it is set in an atmosphere of steam.

A standard tennis ball rubber core 4 is sprayed with a solution'of balata in triehlore'thylene to cover the core surface with an adhesive layer after 5 approximately 0.03 thick. A single covering 01 a composite yarn I is then wound onto the core 4 in a spiral winding starting and finishing at diametrically opposite points on the surface of the core, the coils of the spiral winding'being contiguous so that the'composite yarn substantially covers the core.

The covered core is placed in a mold which is then closed and heated at 110 C. for ten minutes, thus causing an increase in the pressure of a gas within the inflated core. The ball is thus molded under heat and pressure and the rubber coating on the core becomes plastic and penetrates into the coils of the composite yarn; thus ensuring satisfactory adhesion of the wool fibers to the core. During molding the cellulose acetate 2 softens and helps to. elfect adhesion of the fibers to each other. I

After molding, the wool on the surface of the ball is raised by scratching with a wire brush or by-placingthe ball'ina rotating drum lined with card clothing, or by any'other suitable method such as raising with wires similar'to' those used in a conventional wool raising machine. The helical formation of the roving of the composite yarn is destroyed during raising as the strands of the roving are broken on the side of the yarn remote from the rubber'core. Felting of the core covering is then carried out by milling the ball in a 10% sodium oleate solution for about 40 minutes, the surface of the core being repeatedly distorted to cause migration and felting of the wool'fib'ers to form a felted cover 5 as shown in Fig. 4. The ball is washed after felting and then treated with an aqueous dispersion of polymethyl Ine'thacrylate and given a final molding to impart to'the surface a finished appearance, the mold marks being subsequently removed by steaming the ball in wet steam at C. for two minutes. Treatment with a dispersion of polymethyl methacrylate is optional but in the case of a treated ball the polymethyl methacrylate softens during molding and helps to consolidate the felt by assisting adhesion between fibers in the covering.

The thickness of the composite yarn is determined'by the'thickn'ess of the WOOll'OViIlg, and the number of turns per inch of the helix of roving on the central thread is arranged to pro- 'Vide' contiguous turns. In order to produce a finished ball which conforms to ofiicial requirementsthe composite yarn is made sufficiently thick and of such density as to allow for unavoidable losses of-wool fibers during the raising and' felti ng operations.- Instead of covering the core 4 with a single "7 0 spiral winding of composite yarn I as described, a single covering of composite yarn may be applied in two spiral windings starting from diametrically opposite points on the core and meeting in a plane approximately midway between said points.

Before raising the surface of the yarn covered core, the coils of the composite yarn may be cut by tumbling the ball in a drum having the cutting edges of razor blades projecting from the inner surface of the drum by an amount equal to the depth of cut required, preferably half the thickness of the wool coil.

In an alternative method according to the invention of making a tennis ball, composite yarn is made from eight singles of wool yarn of 6s West of Englands count, each with an initial twist of 3.5 2 T. P. I. which are twisted together with 1.5 S T. P. I. and wound on a central sodium alignate thread in the form of a left circular helix having 6.75 coils per inch, which for the yarn used. gives a close spiral on the central thread. An adhesively coated rubber core is wound with a single spiral covering of the composite yarn and molding, raising and felting are carried out substantially as described in connection with a previous example. In this case, however, the central alignate thread is dissolved during the felting operation to leave only a wool covering on the rubber core.

In many cases, it has been found advantageous to apply adhesive solution to the surface of the composite yarn as well as to the rubber core. This may be done conveniently by winding composite yarn in a close helix on a circular drum about six inches in diameter, steaming the yarn to relax it and at the same time compressing the coils axially of the drum to form the yarn into substantially square cross section, allowing the yarn to dry and then applying adhesive solution to the outside surface of the yarn on the drum. Not only is this method convenient for the application of adhesive to the yarn, but the setting of the yarn into a substantially square cross section during steaming means that when the yarn is spirally wound on the rubber core adjacent coils lie flush against each other and provide a more uniform covering for the core than composite yarn of more or less circular cross section.

As an alternative to covering a rubber core by winding composite yarn directly thereon the yarn may be preformed into panels for adhesion to the rubber core. Each panel is formed by winding a length of composite yarn upon itself in substantially square formation. The panels are preferably formed in pairs, one being wound outwards from a central starting point, and the yarn forming this panel being continued to form a similar panel wound inwards to a central finishing point. One side of each pair of panels is painted with resin or rubber solution to maintain the coils of the panels in position while fixing the panels on a rubber core. Two pairs of panels are formed around and stuck to the rubber core substantially to cover it, the material of the cover then being molded, raised and felted as previously described.

A proportion of polyamide fibers, e. g. nylon, or polyester fibers, e. g. Terylene, or other nonfeltable fibers may be introduced into the material of the composite yarn but the yarn must comprise a substantial proportion of material which felts satisfactorily, the commonest example being wool fiber, though certain otheranimal fibers are also suitable. When the composite yarn comprises a proportion of thermoplastic synthetic fibers which soften during molding these help to consolidate the felt by assisting adhesion between fibers in the finished covering. In general a satisfactorily felted surface is not obtainable with composite yarn containing more than 50% of non-feltable fiber and it is preferred to use not less than two parts of wool fiber to one of non-feltable fiber.

Many alternatives are available for the central thread of the composite yarn. The thread may be a cellulose acetate or soluble alignate as previously instanced or any other convenient synthetic thread. Alternatively a central wool thread may be employed.

Instead of making composite yarn by winding a single helix of yarn or roving on the central thread, several helices may be used. Alternatively a number of ends of roving may be braided round the central thread.

For sticking the composite yarn to the rubber core, instead of balata solution as described, adhesives such as rubber solution, rubber dough or a thermoplastic or thermosetting resin applied, for instance as a solution in an organic solvent, may be used.

The method of making a tennis ball according to the present invention eliminates the cutting out and fitting to a core of felt panels, and this eliminates the wastage of felt left over after cutting out such blanks. Furthermore the composite yarn used in the present invention is inexpensive as compared with the felted fabric used in the conventional ball and all waste wool can be re-carded and used again. These economies lead to a cheaper product and the ball produced by the present invention does not suffer from the initial change in playing characteristics as does a conventional ball during shaking down of the felt panels on the core.

Having described our invention, what we claim 1. A method of making a textile covered ball having an inflated core which comprises covering an inflated core with a single thickness of composite yarn comprising a central thread wrapped with a helix of feltable material, effecting adhesion of the yarn to the core and raising and felting the covering in position on the core.

2. The method of claim 1 wherein the covered core is molded under heat and pressure before raising and felting the covering.

3. The method of claim 1 wherein the wrapping on the central thread comprises at least two parts of wool to one part of ncn-feltable fiber.

4. The method of claim 1 wherein the wrapping is composed solely of wool.

5. The method of claim 1 wherein the composite yarn, before application to the core, is compressed into substantially square cross-sectional form which is fixed by steaming the yarn.

6. The method of claim 1. wherein the central thread is soluble in a solvent in which said feltable material and core are insoluble and in which said thread is dissolved from said covering after adhesion to said core from the composite yarn during felting.

7. The method of claim 6 wherein the central thread is alginate thread soluble in an aqueous medium.

8. The method of claim 1 wherein the central thread is a cellulose acetate thread.

9. The method of claim 1 wherein the central thread is a wool thread.

10. The method of claim 1 wherein the core cover, after raising and felting thereof, is molded to the required shape of the finished ball.

11. The method of claim 10 wherein the core cover, after raising and felting thereof, is treated with an aqueous dispersion of polymethyl methacrylate before molding.

12. The method of claim 1 wherein after the composite yarn has been applied to the core, the coils of the yarn or roving wrapped about the central thread are cut on the side remote from the core before raising and felting.

JOHN ANDERSON. RONALD STANSFIELD GOY.

References Cited in the file of this patent UNITED STATES PATENTS Number Number 6 Penfold July 5, 1932 Ellis Dec. 10, 1935 Roberts Aug. 13, 1940 Roberts Sept. 1, 1942 Radford Oct. 27, 1942 Chagnon July 15, 1947 FOREIGN PATENTS Country Date Great Britain Mar. 16, 1925 Great Britain -1 Oct. 4, 1935 Great Britain Jan. 2'7, 1936 France June 2'7, 1949 

